The present invention relates to cache control for transferring data from a hard disk to a cache efficiently, enhancing a hitting rate of the cache, shortening a command execution time, and enhancing a data transfer rate.
In a hard disk, the efficiency of data transfer to a host is improved by providing a cache, then transferring data from the disk to the cache, and managing the data so that the data can be transferred from the cache directly to the host. One cache area is further divided into several areas, and data to undergo a process of a different nature, or data of a different nature is written in a classified condition into each area. This improves the hitting rate of the cache, and enhances data transfer efficiency.
For example, there are schemes in which the hitting rate is improved by extracting random, sequential, or other access patterns, and allocating a cache area for each pattern. These cache control schemes are described in documents such as Patent Documents 1, 2, and 3. There is also a scheme in which data is distributed to two cache areas obtained by division based on statistical processing results relating to a data access status. Such a cache control scheme is described in Patent Document 4. In yet other schemes, cache areas are set and managed for each program or thread, for example, and these cache control schemes are described in documents such as Patent Documents 5 and 6. The Patent Documents are listed as follows:
Patent Document 1: Japanese Patent Laid-Open No. Hei 7-105095
Patent Document 2: Japanese Patent Laid-Open No. Hei 10-301847
Patent Document 3: Japanese Patent Laid-Open No. Hei 10-254778
Patent Document 4: Japanese Patent Laid-Open No. Hei 5-189316
Patent Document 5: Japanese Patent Laid-Open No. 2001-101076
Patent Document 6: Japanese Patent Laid-Open No. 2000-56993.